Although it would be desirable to avoid high moisture contents to prevent deterioration of the building structure, and at the same time to provide constant humidity the year round to minimize dimensional and other changes in materials and furnishings within a building, this is difficult to achieve under Canadian winter conditions. The morning humidity readings are taken at 6:00 am local standard time.
If one has concerns about a packaged collection stored in a room with frequent damp periods, then continual monitoring of many, or all bags, is necessary, and the colour indicators strips may be the only reasonable alternative (aside from fixing the room RH).
most case-bound books. In buildings with large moisture sources steps may have to be taken to eliminate water vapour from them to avoid condensation.
Corroded metals lose their original surface.
Active machinery – humidifiers and dehumidifiers – respond minute by minute via their humidistats.
"Zip-Loc" TM. The tables give the daily relative humidity, averaged for the year. The answer to both questions is "no." Any object known to have been at least once at some very low RH, say 10% RH, or at least once at some high RH, say 80% RH, is not susceptible to further mechanical damage from one more event of the same magnitude, since any fractures, delaminations and irreversible compressions will have already taken place (unless it is known to have weakened significantly from other causes in the interim).
These objects will remain damp far longer than if they had been left open. Since fracture can accumulate via fatigue, "severe" damage may be reached by several thousand cycles of "small" or several million cycles of "tiny."
Table 1. 100% RH, is ~36 grams per cubic meter, whereas at 20°C it is only ~18 grams per cubic meter, at 10°C it is ~9 grams per cubic meter, at 0°C it is ~4 grams per cubic meter, and so on. How can temperature and humidity variations affect my health? If it is in a leaky box, such as one with a 1mm crack at the top and the bottom seams, then adding one of the recommended ratios of silica gel from the literature will make little difference, and cost much more than just repairing the crack. Precipitation: 0.73" Humidity: 62%.
. Again, why bother with the elaborate mechanical control?
J. Lstiburek is the leading expert in North American on moisture control in buildings, and the role of vapour barriers and air barriers. If the droplets are on top, the problem is warm humid air entering the basement and forming condensation on the wall.
pp. It is important to realize that what is normally referred to as "humidity" is actually relative humidity.
There is little conclusive evidence to show that either high or low humidities are of themselves detrimental to the health of normal people. Note that fluctuation to higher RH may not always cause visible damage, since many joints, panels are invisibly crushed, but this makes them more likely to split during lower RH. Note also that stable RH is not a good thing if it is a stable RH just within the danger zone of Figure 4. Lstiburek and Carmody (
The formation of a solution by certain salts that absorb moisture from the air above a critical RH value. It rarely gets really warm here and you can safely leave your swimwear at home. It has been determined that the average family of four will produce by its normal activities within a house about 0.7 pounds of water vapour per hour, but that this may rise to as much as 2 pounds per hour on wash days. The normal humidity levels in January at Canada's largest cities are listed below. The tables give the month's daily average relative humidity. Most mould damage remains. Not to be confused with hydrometer, a device to measure the density of a liquid. If one is not convinced by this model of fluctuation damage and its predictions of risk, as in Table 1, one can draw instead upon the concept of a "proofed fluctuation".
In areas where very damp conditions alternate with dry conditions, whether daily, seasonally, or both, packaging will eliminate the daily fluctuations and reduce the seasonal fluctuations. Canadian Climate Normals. It is a measure of the amount of water vapour present in the air expressed as a percentage of the maximum amount that the air can hold at that particular temperature. This situation is typical of many that occur in buildings and when fully understood gives much insight into many humidity problems. Often, one will find that only a small and manageable part of the collections is at significant risk from incorrect RH. While large houses with high ventilation rates will have low humidities unless humidifiers are used, it is probable that a large proportion of the houses now being constructed have sufficient humidity provided by natural sources within the house. 2007
The corresponding outdoor relative humidities at each location are about the same - 88 percent. 35-41. From a practical risk assessment perspective, the many forms of incorrect RH can be subdivided into four types: Each of these will be explained in detail under "Deterioration". Moderate risk of mechanical damage to high vulnerability objects, tiny risk to most paintings, most photographs, some objects, some books and no risk to many objects and most books.
Common experience teaches us that basements, or the ground floor of buildings with no basement, are associated with damp. ASHRAE. 21.1-21.16.
It is not impossible (in the colder areas of Canada), with poor vapour control in a wall or ceiling, to collect as much as one pound of frost per square foot of wall or roof area. Most of the types of incorrect RH depend on the pattern over time.
Table I. If you truly need an average RH, especially over longer time intervals, the better practice is to use the average observed and saturation vapor pressures to calculate RH over each time interval.
Even moderate humidities inside buildings can produce wetting by condensation on and in the building structure because of the large temperature gradients within walls in winter. . When monitoring the collection itself for signs of mechanical damage, great care must be taken in interpreting symptoms. Thanks to the Centro Nacional de Conservación y Restauración in Chile, the Canadian Conservation Institute’s web resource Agents of deterioration, translated into Spanish by ICCROM, is now available free of charge. Humidity is one of the most important of the topics that are of special concern in Canadian building design and operation. Damp causes mould, which disintegrates or discolours skin, leather (Figure 1), textiles, paper, basketry, and occasionally wood, paint, and glass. When cooled to 49°F the mixture becomes saturated; if cooled further, water will be removed by condensation on the window surface.
When the temperature is changed, the relative humidity changes, since the capacity of the air for holding moisture increases with increasing temperature. Technical Bulletin 33. Taking all this information into account, Table 1 summarises our current best estimate of the likelihood of mechanical damage from various ranges of fluctuation (in the portion labeled "RH fluctuations"). Further cooling results in condensation on objects. "Small" usually needs careful inspection to notice the damage, "tiny" needs magnification. Far better for a collection stuck most of the time at 70% RH to have its RH fluctuate down to the safe zone every few days, since it will reset the mould growth clock back to zero.